How to Read an Eyeglass Prescription: Complete Guide

Learning how to read an eyeglass prescription for the first time can feel like decoding a secret message. Terms like SPH, CYL, AXIS, ADD, and PD may seem like foreign concepts — but once you understand what each number means for your actual vision, ordering prescription glasses online becomes straightforward and confident. This guide explains every field on a standard eyeglass prescription, what the numbers reveal about your eyes, and how to enter your prescription manually at FuzWeb to order with complete confidence.

How to Read an Eyeglass Prescription: What You Need to Know

An eyeglass prescription is a written specification issued by an optometrist or ophthalmologist after a comprehensive eye examination. It defines the precise corrective power required for each eye to achieve clear vision. Unlike a contact lens prescription, an eyeglass prescription does not include base curve or diameter measurements — it contains only the optical correction values needed to manufacture your lenses.

A standard eyeglass prescription contains two rows of data — one for each eye — and a set of abbreviations that are consistent across opticians worldwide. Your prescription is valid for a defined period — typically one to two years depending on your country and optician. Always use a current prescription when ordering prescription glasses online.

OD and OS — Which Eye Is Which

Every prescription is divided into two rows. OD stands for oculus dexter — Latin for right eye. OS stands for oculus sinister — Latin for left eye. Some prescriptions use RE (right eye) and LE (left eye) instead, but OD and OS are the international standard. Always enter OD values in the right eye row and OS values in the left eye row. Swapping them will produce lenses that correct the wrong eye — one of the most common ordering mistakes.

SPH — Sphere: What It Means for Your Vision

SPH is the primary corrective power of the lens, measured in dioptres (D). It corrects nearsightedness (myopia) and farsightedness (hyperopia). A minus sign (−) before the number indicates myopia — you see clearly up close but struggle with distance. A plus sign (+) indicates hyperopia — you see more clearly at distance but struggle up close. If the SPH field shows PL or Plano, it means zero correction is needed for that eye.

SPH values typically range from −20.00 to +20.00, though most prescriptions fall between −6.00 and +4.00. To put this in perspective: an SPH of −1.00 means you can see clearly up to about one metre without glasses. An SPH of −4.25 means your clear vision range without correction is roughly 23 centimetres — about the distance from your eye to your hand. The higher the number, the stronger the correction required.

CYL — Cylinder: What It Means for Your Astigmatism

CYL corrects astigmatism — an irregularity in the curvature of the cornea or lens that causes blurred or distorted vision at all distances. Not everyone has astigmatism. If the CYL field on your prescription is blank or shows DS (dioptre sphere), you have no astigmatism correction and can leave the CYL field empty when ordering.

Like SPH, CYL values carry a plus or minus sign and are measured in dioptres. Negative CYL is the most common format used by optometrists in North America and most of Europe. A high CYL value — anything above −1.50 — typically means you experience noticeable distortion or ghosting around objects, particularly at night or in low contrast conditions. Correcting it with the right lens makes a significant difference to visual comfort.

AXIS — The Direction of Your Astigmatism

AXIS is only relevant when a CYL value is present. It defines the orientation of the astigmatism correction — the angle at which the cylindrical power must be positioned in the lens. AXIS is measured in degrees from 1 to 180. There is no plus or minus — it is always a positive integer.

Think of AXIS as a compass bearing for your astigmatism. An AXIS of 90 means the correction runs vertically. An AXIS of 180 means it runs horizontally. The optical technician uses this value to align the cylindrical correction precisely with your cornea’s irregularity. Even a small error in AXIS placement can cause blurred or tilted vision — which is why entering it accurately when ordering online matters. If your prescription has a CYL value, it will always have a corresponding AXIS value. If CYL is blank, AXIS is irrelevant and should be left empty.

ADD — Addition: For Progressive and Reading Lenses

ADD is the additional magnifying power added to the lower portion of a progressive or bifocal lens to correct presbyopia — the age-related loss of near focusing ability that typically begins in the mid-40s. ADD is always a positive value, typically between +0.75 and +3.50.

Understanding ADD is crucial for anyone who needs multifocal lenses. It ensures the lens provides adequate magnification for comfortable reading and close-up tasks while maintaining distance correction in the upper zone. If you are ordering single vision lenses, ADD does not apply and the field will be blank on your prescription. If you are ordering progressive lenses, ADD is required — do not leave it blank.

PD — Pupillary Distance: Why It Matters More Than You Think

Pupillary distance (PD) is the distance in millimetres between the centre of your left pupil and the centre of your right pupil. It tells the optical lab where to centre the prescription in each lens. Without an accurate PD, even a perfectly written prescription will produce lenses that sit off-centre, causing eye strain, headaches, and distorted vision.

PD can be recorded as a single combined measurement — for example, 63 mm — or as two separate values for each eye (dual PD) — for example, 31.5 R / 32.0 L. An incorrect PD measurement can result in discomfort and reduced effectiveness of your prescription lenses, so accuracy here is as important as the prescription values themselves.

If your PD is not on your prescription, use the Find your PD link in the FuzWeb manual entry form to measure it in under two minutes using your smartphone. For a full step-by-step guide, read How to Measure PD at Home.

Segment Height — For Bifocal and Progressive Lenses

Segment height is relevant for anyone ordering bifocal or progressive lenses. It refers to the vertical measurement from the bottom of the lens to the top of the near or intermediate vision segment. In progressive lenses, the lower portion of the lens is dedicated to near or intermediate vision, while the upper portion corrects distance vision.

Accurate segment height ensures that the near vision zone is positioned correctly relative to your pupil when you look down to read. If segment height is set too high or too low, you will find yourself tilting your head uncomfortably to access the reading zone. Your optician measures segment height when fitting your frames — it is frame-specific and cannot be determined from your prescription alone. At FuzWeb, our optical team handles segment height based on your frame selection.

Intended Use — Distance or Near

At FuzWeb, the manual entry form includes an Intended Use field with two options: Distance and Near. Select Distance for standard everyday glasses. Select Near only if your optician has written a dedicated reading prescription. If you are ordering progressive lenses, select Distance — the ADD value handles the near correction automatically.

How to Enter Your Prescription Manually at FuzWeb

Once you understand your prescription, entering it at FuzWeb takes less than two minutes. Here is the exact process:

Step 1 — Select your frame and start the lens process. On any frame product page, select Select Lenses and Purchase. Choose your lens type — single vision or progressive — on the first screen.

Step 2 — Choose Enter Manually. On the prescription submission screen, you will see four options: Upload a File, Enter Manually, Use Prescription on File, and Email Later. Select Enter Manually.

Step 3 — Enter your OD values. In the OD (Right Eye) row, enter your SPH, CYL, and AXIS values from your prescription using the dropdown menus. If you have an ADD value and are ordering progressive lenses, enter it in the ADD field. If CYL is blank on your prescription, leave the CYL and AXIS fields empty.

Step 4 — Enter your OS values. Repeat the same process for the OS (Left Eye) row using the left eye values from your prescription.

Step 5 — Select Intended Use. Choose Distance for everyday glasses or Near for dedicated reading glasses. If ordering progressives, select Distance.

Step 6 — Enter your PD. Select Single PD or Dual PD and enter your measurement. If you do not have your PD, tap Find your PD to measure it with FittingBox.

Step 7 — Continue to lens options. Once all fields are complete, proceed to select your lens index, coatings, and any upgrades. Your prescription data is saved for this order.

Common Mistakes When Entering a Prescription Online

Swapping OD and OS — the most common error. OD is always right eye, OS is always left eye. Double-check before submitting.

Entering CYL without AXIS — if you have a CYL value, AXIS is always required. Check your prescription for both values.

Leaving ADD blank on a progressive order — ADD is mandatory for progressive lenses. If your prescription does not show an ADD value, confirm with your optician before ordering.

Entering PD as dual when you only have single — if your prescription shows one PD number, enter it as Single PD. Do not split it manually unless you have measured dual PD directly.

Using an expired prescription — prescriptions expire. Using outdated values will produce lenses that no longer match your current vision needs.

Frequently Asked Questions

What does a minus sign mean on my prescription? A minus SPH value means you are nearsighted — you see clearly up close but struggle with distance. A minus CYL value indicates the direction of astigmatism correction. Both are standard and very common.

My prescription has no CYL or AXIS — is that normal? Yes. Not everyone has astigmatism. If CYL is blank, leave those fields empty when ordering. Do not enter zero — leave them unselected.

What if my prescription shows DS instead of a number? DS stands for dioptre sphere — it means no cylindrical correction is needed for that eye. Treat it the same as a blank CYL field.

Can I order progressive lenses if my prescription does not show an ADD value? No. Progressive lenses require an ADD value. If your prescription does not include ADD, you need a new eye examination or a dedicated reading prescription from your optician.

What is the difference between single vision and progressive lenses? Single vision lenses correct one focal distance — either distance or near. Progressive lenses correct both in a single lens with a gradual transition between zones. If you are over 40 and need correction for both distances, progressive lenses are the standard recommendation.

My prescription has positive CYL values — what do I do? Some opticians use plus CYL notation instead of minus CYL. If your CYL values are positive, contact us before ordering — we can transpose the prescription to the correct format for lens manufacturing.

Is it safe to order prescription glasses online? Yes — provided you enter your prescription accurately and have a current PD measurement. If your lenses are incorrect — confirmed by a lensometer readout from any local optician — we replace the pair within 14 days of delivery.

Ready to Order?

Now that you understand every number on your prescription, you have everything you need to order with confidence. Browse over 1,079 frames across acetate, titanium, TR-90, and metal — complete pairs with prescription lenses from $74.98. UV400, anti-reflection, and HMC coating included as standard on every lens.

For further reading: How to Measure PD at Home — The Best Glasses for Your Face Shape — Glasses Frame Measurement Guide